1. Field of the Invention
This invention relates generally to a novel humidity sensor having a flexible insulator film with two electrodes thereon.
This invention is directed more particularly to a humidity sensor which detects a dew precipitated thereon in an ambient atmosphere at the dew point and which is suitable for detecting humidity at the main parts of electronic instruments such as the tape guide portion of a VTR which dislike the formation of dew-drops or detecting the appearance of dewdrops on the window glass of vehicles.
This invention is directed also to a video tape recording and/or reproducing apparatus employing the humidity sensor mentioned as above.
2. Description of the Prior Art
In a magnetic recording and/or reproducing apparatus having a guide means for guiding a recording medium such as a magnetic tape by winding the magnetic tape on the guide means, if its ambient temperature is varied, dewdrops are precipitated on the surface of the guide means. When the dewdrops are formed on the surface of the guide means, the magnetic tape adheres to the surface of the guide means, which results in that the tape can not travel normally. Further, due to the dewdrop or humidity on the surface of the guide means, the tape itself is deformed frequently and hence undesired phenomena such as so-called jitters and skews are apt to be caused.
In the art, there has been proposed a humidity sensor having a resistor, whose resistance value is changed in accordance with the state of dewdrops appeared thereon, fitted on the surface of the tape guide member for detecting the state of dewdrops as a variation of the resistance value of the resistor.
One of practical examples of the prior art humidity sensor has a dew detecting element on the peripheral surface of a helical guide of a tape guide drum for deriving the humidity of whole the drum as a variation of electric resistance value and a level detecting circuit including the detecting element an output signal from which is used to control the operation system of a VTR suitably.
With such a prior art humidity sensor, when dewdrops appear on the tape guide drum, tape guide members and the like, the above undesired phenomena can be avoided by some extents. However, the sensitivity or response of the dew detecting element to the humidity of the prior art is a problem. The reason why the resistance between a pair of electrodes is varied by humidity is that the pair of electrodes are bridged by the dewdrops. In practice, however, even when fine particles of dewdrops appear between the electrodes, there is the case that no output signal is fed from the output terminals of the humidity sensor to the following stage of an amplifier.